The process of extruding thermoplastics to form a wide variety of articles is well known in the art. Extrusion has been employed to produce sheets, films, pellets and wire and cable coatings, as well as other products. Typically, the thermoplastic is fed to an extruder wherein the thermoplastic is melted and then the melt is forced through a shaping die under pressure.
One of the drawbacks associated with the extruding of sheets and other articles is the problem of the need to change the die when a different width article is desired. Removing the die and replacing it with a new die of different dimensions has proved to be cumbersome and cause a lot of down time on the extruder.
The use of adjustable deckles has been disclosed in the prior art to facilitate the altering of the width of the die and the extruded article. For example, Ryan et al., U.S. Pat. No. 3,320,634 disclose the use of adjustable deckle plates to change the die configuration. Chiselko et al., U.S. Pat. No. 3,293,689 teach the use of tracks to move deckle bars in order to regulate the width of extruded sheets. Another patent disclosing the use of adjustable deckles is Melead, U.S. Pat. No. 3,829,274.
Maejma, U.S. Pat. No. 4,978,289 discloses a process control system to adjust lip-width adjusting devices on the basis of a correction signal to provide uniformity in the width of the extruded article.
However all of these disclosures still require the use of mechanical devices to change the configuration of the die through which the molten thermoplastic flows. It would represent a notable advance in the state of the art if a means for altering the width of extruded articles could be provided which did not require mechanical manipulation of the die configuration.
To this end, the present applicant has found that the width of an extruded article can be altered without the need for mechanical modification of the extruder die. Such a notable advance enables the user to change the width of the extruder article while the extruder remains on line and does not result in any down time.